Gait initiation (GI) difficulty is a common problem in individuals with Parkinson's disease (PD), often linked to impaired anticipatory postural adjustments (APA). Currently, there are no targeted rehabilitation programs designed specifically for GI-related APA in PD patients. Research has shown that while motor learning deficits are common in PD, explicit learning is better preserved than implicit learning. Therefore, a GI-related APA training system using an explicit learning model could be particularly effective for this population. During motor learning, long-term potentiation (LTP) increases the excitability of the primary motor cortex. Paired associative stimulation (PAS) has been demonstrated to induce LTP-like changes in the motor cortex, making it a potential priming method to enhance motor learning. However, the priming effect of PAS targeted at leg muscles and the motor cortex on motor learning related to GI-APA has not been previously studied. The objectives of this study are: 1. To investigate the effects of explicit and implicit training on GI-related APA. 2. To evaluate the priming effect of PAS on GI-related APA training and the associated plasticity changes in the motor cortex.